The present invention relates to a counterweight handling system for load handling equipment, and more particularly to a counterweight handling system for ring-supported lift cranes.
Efforts to increase the lift capacity of cranes without requiring extensive modification of the basic crane components led to the development of an auxiliary support for cranes as disclosed in U.S. Pat. No. 3,485,383. This invention used an annular circular support, often called a ring, on which the load handling boom and counterweight were both supported on rollers. The basic crane upper works and lower works fit within the ring and the lower works was connected thereto. The upper works was rigidly connected to the boom and counterweight so that as the upper works swung with respect to the lower works, the boom and counterweight traveled around the ring. In this way a basic crane could be outfitted to handle larger lifts because the distance between the pivot point of the boom and the counterweight was increased and, since the counterweight was not carried on the upper works, larger amounts of counterweight could be used without modification of the upper works and its ring gear connection to the lower works.
Numerous other crane designs have taken advantage of the ring support system. For example, see U.S. Pat. Nos. 4,483,448; 4,196,816; 4,387,814; and 4,446,976. Cranes built by the Manitowoc Company, Inc. that use this system use the trademark RINGER, and such cranes are often referred to as RINGER cranes.
The ring allows the crane to swing when it is in position at a job site, and thus pick up a load and move it to its placement position. To move a ring-supported lift crane from one lift site to a second lift site, however, requires removing the counterweight from off of the support ring. If the second site is near to the first site, conventional crawler type tracks on the lower works are used to move the crane, with the ring attached, to the second lift site.
Because most cranes are moved between construction jobs, the cranes are designed to be transported, which means that they are made of components that meet weight limits imposed on highway transportation. Thus, typically the counterweight is made of numerous counterweight units. For example, a crane having removable counterweights with a total weight of 1,144,000 pounds could use 26 counterweight units or boxes of 44,000 pounds each, which is a convenient weight for an assist crane and is the maximum allowable transport weight for many highways.
When it is time to move a ring-supported lift crane from one lift site on a construction job to another site, an assist crane is used to unload counterweight units one at a time and set them aside. Then after the crane and ring had been repositioned, the assist crane makes repeated trips between the sites, moving the individual counterweight units and restacking the counterweight units onto the counterweight carrier of the repositioned crane. While the counterweight moving procedure is time consuming in and of itself, the overall length of time it takes to reposition the ring-supported lift crane is dependent on this procedure because removing the counterweight units must take place before many other steps of preparing the crane for repositioning can occur, and reinstalling the counterweight has to wait until after the reverse of those many steps has taken place. Thus there is a need for an improved counterweight handling system for ring-supported lift cranes.